[llvm] BPF: Change callx insn encoding (PR #81546)

[via llvm-commits]

https://github.com/yonghong-song created https://github.com/llvm/llvm-project/pull/81546

Currently, the kernel verifier unsupported callx insn used the 32-bit imm field to store the target register. On the other hand, gcc used the dst_reg field to store the target register. The gcc encoding is better. This patch adjusted the coding to be the same as gcc.

>From c703a709fe16af9f3896e8117ad7d710279d3ff5 Mon Sep 17 00:00:00 2001
From: Yonghong Song <yonghong.song at linux.dev>
Date: Mon, 12 Feb 2024 13:58:06 -0800
Subject: [PATCH] BPF: Change callx insn encoding

Currently, the kernel verifier unsupported callx insn
used the 32-bit imm field to store the target register.
On the other hand, gcc used the dst_reg field to store the target register.
The gcc encoding is better. This patch adjusted the coding
to be the same as gcc.

Signed-off-by: Yonghong Song <yonghong.song at linux.dev>
---
 llvm/lib/Target/BPF/AsmParser/BPFAsmParser.cpp | 1 +
 llvm/lib/Target/BPF/BPFInstrInfo.td            | 4 ++--
 llvm/test/MC/BPF/insn-unit.s                   | 3 +++
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Target/BPF/AsmParser/BPFAsmParser.cpp b/llvm/lib/Target/BPF/AsmParser/BPFAsmParser.cpp
index 90697c6645be2f..0d1eef60c3b550 100644
--- a/llvm/lib/Target/BPF/AsmParser/BPFAsmParser.cpp
+++ b/llvm/lib/Target/BPF/AsmParser/BPFAsmParser.cpp
@@ -229,6 +229,7 @@ struct BPFOperand : public MCParsedAsmOperand {
     return StringSwitch<bool>(Name.lower())
         .Case("if", true)
         .Case("call", true)
+        .Case("callx", true)
         .Case("goto", true)
         .Case("gotol", true)
         .Case("*", true)
diff --git a/llvm/lib/Target/BPF/BPFInstrInfo.td b/llvm/lib/Target/BPF/BPFInstrInfo.td
index 7d443a34490146..690d53420718ff 100644
--- a/llvm/lib/Target/BPF/BPFInstrInfo.td
+++ b/llvm/lib/Target/BPF/BPFInstrInfo.td
@@ -622,9 +622,9 @@ class CALLX<string OpcodeStr>
                    (ins GPR:$BrDst),
                    !strconcat(OpcodeStr, " $BrDst"),
                    []> {
-  bits<32> BrDst;
+  bits<4> BrDst;
 
-  let Inst{31-0} = BrDst;
+  let Inst{51-48} = BrDst;
   let BPFClass = BPF_JMP;
 }
 
diff --git a/llvm/test/MC/BPF/insn-unit.s b/llvm/test/MC/BPF/insn-unit.s
index 58342cda7cc0ad..224eb7381aa234 100644
--- a/llvm/test/MC/BPF/insn-unit.s
+++ b/llvm/test/MC/BPF/insn-unit.s
@@ -61,6 +61,9 @@
 // CHECK-32: c3 92 10 00 00 00 00 00 	lock *(u32 *)(r2 + 16) += w9
 // CHECK: db a3 e2 ff 00 00 00 00 	lock *(u64 *)(r3 - 30) += r10
 
+  callx r2
+// CHECK: 8d 02 00 00 00 00 00 00 	callx r2
+
 // ======== BPF_JMP Class ========
   if r1 & r2 goto Llabel0    // BPF_JSET  | BPF_X
   if r1 & 0xffff goto Llabel0    // BPF_JSET  | BPF_K